The disclosures herein relate generally to dental implants and more particularly to a screw form dental implant having a variable profile thread.
Many current screw-form dental implants are well designed for use in dense bone. For example, the implant disclosed in U.S. Pat. No. 5,897,319 has sharp cutting features at their apical ends that readily facilitate self-tapping into hard bone.
The osseous anatomy of the human jaw is complex. While the density of the bone in the anterior regions of the mandible and maxilla is high, the posterior regions, particularly in the maxilla, are of significantly lower density. The height of the bony ridge in the posterior maxilla can be greatly reduced in partially or totally edentulous patients. This can lead to the need for use of shorter dental implants or grafting procedures in the nasal sinus in order to increase the height of bone available for implant placement.
The nasal sinus is lined by a membrane called the nasal or schneiderian membrane. Damage to this membrane during implant placement must be avoided. In the mandible, the mandibular nerve is located within the mandibular canal. Damage to the mandibular nerve must also be avoided. Inadvertent placement of a dental implant into the mandibular canal increases the risk of mandibular nerve damage, particularly if the implant has sharp surfaces at its apical end.
Dental implant stability in low-density bone, such as that found in the posterior regions of the mandible and maxilla, can be difficult to achieve. Compaction of low density bone, such as by the use of osteotomes, is commonly performed in order to enhance the stability of implants at the time of surgical placement. Low density bone can also lead to the problem of placing dental implants too deeply into the jaw, because commonly available implants have a fairly continuous geometric shape, be it cylindrical or tapered, up to the point that is ideally placed at the crest of the bone.
Implants of various tapers and with various thread profiles are known in the art. For example, U.S. Pat. No. 5,427,527 describes a conical implant design that is placed into a cylindrical osteotomy site in order to induce bone compression at the coronal aspect of the implant, i.e. at its widest end.
A variety of thread profiles and patterns are known in the art. The most common design involves a symmetrical, V-shaped appearance such as that illustrated in U.S. Pat. No. 5,897,319. A variable thread profile is disclosed in U.S. Pat. Nos. 5,435,723 and 5,527,183 which is mathematically optimized for stress transfer under occlusal loads. U.S. Pat. Nos. 3,797,113 and 3,849,887 describe dental implants with external thread-like features having a flat shelf facing the coronal end of the implant. U.S. Pat. No. 4,932,868 discloses a thread design with a flat surface disposed toward the apical end of the implant. This thread is not variable over different points of the implant and does not produce both cutting and compression actions as described herein. U.S. Pat. No. 5,007,835 discloses a screw-type dental implant with rounded threads for providing controlled radial osteocompressive force against the walls of a pre-tapped bone site. U.S. Pat. No. 5,628,630 discloses a method for designing dental implants to optimize and control stress transfer to surrounding bone including a thread design that changes from a sharp, highly angled profile at the apical end of the implant to a flat, nearly square profile at the coronal end, the goal being to control the surface area presented to occlusal forces.
Therefore, what is needed is an implant that enhances stability in low density bone such as that formed in the posterior mandible and posterior maxilla.
One embodiment, accordingly, provides a dental implant that is particularly suited for use in lower density bone. To this end, a dental implant having a variable profile thread includes a body having a coronal end and an apical end. The body includes a tapered region adjacent the apical end. A variable width helical thread extends along the tapered region. The thread has an apical side, a coronal side, and a width defined between the apical and coronal sides. The variable width is expanded in the direction of the coronal end. As a result, the least width of the thread is adjacent the apical end and the greatest width of the thread is adjacent the coronal end.
A principal advantage of this embodiment is that a dental implant is provided that addresses the problems described above. It has a unique combination of implant body and thread profile that enhances stability in low-density bone and considers proximity to the sinus membrane and the mandibular nerve.